One equivalent is usually defined as the amount of substance reacted or produced in a red-ox reaction by the transfer of one mole of electrons.
Combustion of methane with oxygen is a convenient example. First write the balanced reaction:
The oxidation state of the carbon atom goes from -4 to +4, and each of the 4 oxygen atoms goes from 0 to -2, so 8 electrons are transferred in this reaction. It may help to think about this by rewriting the reaction to correspond to 1 mole of electrons transferred:
Now it is easy to see that 1/8 mol of methane reacts per mole of electrons. The molar mass of methane is 16 g, so the mass equivalent of methane is
Similarly, the mass equivalent of